Lightweight structural panels are used in the construction industry, and are particularly desired for outdoor use. The ideal panel is lightweight and relatively inexpensive to manufacture, has high insulation qualities, and is weather resistant. An example of a structural panel for housing use, having plastic cover sheets and a foam core, is disclosed in U.S. Pat. No. 4,133,930 to J. Wright (same inventor) and K. Wolfe, issued Jan. 9, 1979.
For heavier commercial and industrial applications, such as forming truck and freight car bodies, automotive panels, and architectural panels, it is desireable to have a structural panel that has sheet metal or metallized cover sheets bonded with adhesive layers to a core of foam or plastic material. It is important that the a good bond is formed between the metal, adhesive, and foam layers of the laminate structure. However, the metal cover sheets of the laminate often have oil spots or chemical films picked up in handling or rust spots which weaken the bond with the adhesive layer, and results in a risk of delamination of the layers. Solvents are typically used to clean the metal surfaces prior to bonding. However, such solvents often contain highly toxic materials and their use results in the production of hazardous wastes.
Accordingly, it is a principal object of the invention to provide a method of forming a good bond between the metal cover sheets, adhesive layers, and foam core of a laminate panel. It is a specific object to remove any oil spots or other chemical films which may appear on the metal sheets, prior to bonding, them with the adhesive layers to the foam core, without the use of toxic solvents. It is also desired to produce a superior structural panel as a result of good bonding techniques.